This dial peer command defines the called number destination or dialed number identification service (DNIS) string. When properly configured, this dial peer command uses the called number to match the incoming call leg to an inbound dial peer.

Called number (DNIS)

gwy(config-dial-peer)# answer-address ANI_string

This dial peer command defines the originating calling number or automatic number identification (ANI) string. When properly configured, this dial peer command uses the calling number to match the incoming call leg to an inbound dial peer.

Calling Number (ANI)

gwy(config-dial-peer)# destination-pattern string

When inbound call legs are matched, this command uses the calling number (originating or ANI string) to match the incoming call leg to an inbound dial peer.

Note: For outbound dial peers, this command is matched against the called number or DNIS strings.

Calling Number (ANI) for inbound or the Called number (DNIS) strings for outbound

gwy(config-dial-peer)# port port

This dial peer command defines the POTS voice port through which calls to this dial peer are placed.

Voice Port

The three call setup elements are:

Call Setup Element

Description

Called number (DNIS)

This is the call destination dial string and is derived from the ISDN setup message or channel associated signaling (CAS) DNIS.

Calling Number (ANI)

This is a number string that represents the origin and is derived from the ISDN setup message or CAS ANI. The ANI is also referred to as Calling Line Identification (CLID).

When the Cisco IOS router or gateway receives a call setup request, a dial peer match is made for the incoming call in order to facilitate routing the call to different session applications. This is not a digit-by-digit match, rather the full digit string received in the setup request is used to match against configured dial peers.

Note: The maximum number of dial peers that can be configured on a Cisco IOS gateway depends on the available memory (DRAM). Each dial peer consumes approximately 6KB of memory. Make sure that you have at least 20% of the total memory reserved for other CPU processes. If the dial peers are used for call routing, a larger number of dial peers will add to the delay to route a call. This will be significant as the Cisco IOS voice stack looks through dial peers from the top down, similar to an Acess Control List.

The router or gateway matches the information elements in the setup message with the dial peer attributes to select an inbound dial peer. The router or gateway matches these items in this order:

Called number (DNIS) with the incoming called-number command

First, the router or gateway attempts to match the called number of the call setup request with the configured incoming called-number of each dial peer. Because call setups always include DNIS information, it is recommended to use the incoming called-number command for inbound dial peer matching. This attribute has matching priority over the answer-address and destination-pattern commands.

Calling Number (ANI) with the answer-address command

If no match is found in step 1, the router or gateway attempts to match the calling number of the call setup request with the answer-address of each dial peer. This attribute can be useful in situations where you want to match calls based on the calling number (originating).

Calling Number (ANI) with the destination-pattern command

If no match is found in step 2, the router or gateway attempts to match the calling number of the call setup request to the destination-pattern of each dial peer. For more information about this, see the first bullet in the Dial Peer Additional Information section of this document.

If no match is found in the step 3, the router or gateway attempts to match the configured dial peer port to the voice-port associated with the incoming call. If multiple dial peers have the same port configured, the dial peer first added in the configuration is matched.

If no match is found in the first four steps, then the default dial peer 0 (pid:0) command is used.

Note: Step 4 is not applicable to voice or dial platforms such as AS5300, AS5350, AS5400, AS5800 and AS5850. If any one of the first three steps is not used, then match dial peer 0, and the call is treated as a dial modem call. This means that customers can get modem tones as opposed to dial tones for inbound calls.

The previous selection process is displayed with this diagram:

The Cisco IOS router or gateway matches only one of these conditions. It is not necessary for all the attributes to be configured in the dial peer or that every attribute match the call setup information. Only one condition must be met for the router or gateway to select a dial peer. The router or gateway stop to search as soon as one dial peer is matched.

The longest prefix matching criteria applies while each step is performed. At each step, if multiple matches are found, the one with the longest explicit match is chosen. This example helps clarify this concept:

Assume the incoming called number (DNIS) is "81690". Dial peer 2 is matched.

If no incoming dial peer is matched by the router or gateway, the inbound call leg is automatically routed to a default dial peer (POTS or Voice-Network). This default dial peer is referred to as dial-peer 0 or pid:0.

Note: There is an exception to this statement. Cisco voice and dial platforms, such as the AS53xx and AS5800, require that a configured inbound dial peer is matched for incoming POTS calls to be accepted as voice calls. If there is no inbound dial peer match, the call is treated and processed as a dial-up (modem) call.

Dial-peer 0 (pid:0) has a default configuration that cannot be changed. The default dial-peer 0 fails to negotiate non-default capabilities, services, and applications such as:

Non-default Voice-Network capabilities: dtmf-relay, no vad, and so forth.

Direct Inward Dial (DID)

TCL Applications

Dial-peer 0 for inbound VoIP peers has this configuration:

any codec

vad enabled

no rsvp support

fax-rate voice

Note: The default DSCP for voice is EF codepoint 101110 (RFC 2598), and the default DSCP for signaling is AF31 codepoint 011010 (RFC 2597). The default dial peer does not mark packets to DSCP 0. All voice packets on the routers are marked by default (this can be overridden by the dial peer), signaling with AF31 and media with EF. Calls that match the default dial peer 0 should also have this behavior.

There are implications for inbound dial peer matching when the isdn overlap-receving command is configured on ISDN interfaces. After every digit is received at the ISDN layer, dial peers are checked for matches. If a full match is made, the call is routed immediately (to the session app in this case) without waiting for additional digits. The 'T' terminator can be used to suspend this digit-by-digit matching and force the router or gateway to wait until all digits are received. The 'T' refers to the T302 interdigit timer at the ISDN level, configurable under the serial interface associated with the ISDN interface. ISDN also provides other mechanisms to indicate the end of digits, such as setting the Sending Complete Information Element (IE) in Q.931 information messages.

Now, assume that an incoming call arrives with no calling number information and is matched with the POTS dial peer based on the destination-pattern 9T command. In this case, the Cisco IOS router or gateway uses the "9" digit as the calling number and forwards the call to the corresponding device, such as CallManager or the IOS Gateway. In order to not replace the empty calling number field, create a dummy POTS dial peer with just the incoming called-number command configured. Because the incoming called-number statement has higher priority than destination pattern for inbound POTS matching, dial-peer voice 2 becomes the POTS dial peer used.

The Warning message shown here, which displays when dial-peer is configured with incoming called-number T, might raise questions in regards to the dial-peer selection with an empty called number from an actual router.

RTR(config)#dial-peer voice 1 pots
RTR(config-dial-peer)#incoming called-number T
Warning: Pattern T defines a match with zero or more digits and hence could
match with an empty number. If this is not the desired behaviour please
configure pattern .T instead to match on one or more digits
RTR(config-dial-peer)#

Incoming dial-peer match with an empty called number:

A "null" called-number is considered "less" qualified compared to a port number and/or in some cases answer-address. Therefore, a match based on a "null" called number will occur ONLY if there is no match based on either answer-address or port-number.

In case of overlap dialing, a "null" called number will not match "incoming called-number T" because timeout has not occurred.

A "null" called-number will match "incoming called-number T" only in case of ENBLOCK and there is no match either because of answer-address and port-number. The warning you see when you configure "incoming called-number T" refers to this specific case.

On DID calls, also referred to as one-stage dialing, the setup message contains all the digits necessary to route the call, and the router or gateway should not do subsequent digit collection. When the router or gateway searches for an outbound dial peer, the device uses the entire incoming dial string. This matching is variable-length by default. This match is not done digit-by-digit because by DID definition, all digits have been received. This example helps clarify this concept:

Assume the DID dial-string is "81690". In this case, the router matches dial peer 4 and forwards the complete dial-string "81690".

This case is also referred to as two-stage dialing. If DID is not configured on the matched incoming dial peer, the router or gateway enters the digit collection mode (digits are collected inband). Outbound dial peer matching is done on a digit-by-digit basis. The router or gateway checks for dial peer matches after the device has received each digit and then routes the call when a full match is made. These examples help clarify this concept:

Assume the dial-string is "81690". Immediately after the router receives the digit "6", the router matches dial peer 3 and routes the call (forwarding only the digits "816").

There are situations where expected dial-strings do not have a set number of digits. In such cases, Cisco recommends you configure the "T" terminator on the dial peer destination-pattern command in order to.use variable-length dial-peers.

The 'T' terminator forces the router or gateway to wait until the full dial-string is received. In order to achieve this, the 'T' terminator forces the router or gateway to wait until the full dial-string is received. The router or gateway:

Waits for a set interdigit timeout before the device routes the call.

Routes the call once the device receives the "#" termination character in the dial-string. For example, if you dialed "5551212#", the "#" indicates to the router that you dialed all the digits and that all digits prior to the "#" should be used to match a dial peer.

This example helps clarify this concept:

Assume the router in this example receives a call setup with dial-string "95551212" from the network. Dial peer 2 then forwards to the PSTN the digits "5551212".

dial-peer voice 2 pots
destination-pattern 9T
port 2/0:23

Now, assume the dial-string from an inbound POTS interface is "81690".

A dial peer operational status must be administratively up and valid for the dial peer to be matched. In order to be considered operational, dial peers must meet one of these conditions: (There are others, but these are the main ones.)

Destination-pattern is configured and a voice-port or session target is also configured.

Every dial plan needs an outgoing and an inbound dial peer. In this document's example, there is a PSTN T1 connection coming as inbound to the maui-gwy-04 router. Here, when an incoming call is received from the PSTN the router tries to find the called number. When the call is received the caller gives the caller ID using the Automatic Number Identification (ANI). In this example, there is a Direct inward dial (DID) range starting from 8. DNIS is the number that the person on the PSTN dials. The number could be an 11 digit or 10 digit number. If it matches the incoming dial peer configured using the direct-inward-dial, only 4 numbers after 8 are forwarded and the rest are stripped of in order for the call to be reached directly without the help of a receptionist.

If you do not have an inbound dial peer configured, Dial-peer 0 is matched and takes care of the call. The Dial-peer 0 has these attributes:

Works for any Codec

Has Voice Activity Detection (VAD) enabled

Marks traffic as IP Precedence 0

Has no RSVP support

Supports FAX-RATE service

Note: The IP Precedence command is set to a default value of 0, which causes the IP precedence to be passed as-is.

show call active voice {brief}—This command displays the contents of the active call table, which shows all of the calls currently connected through the router. In this case, the command is useful in order to display dial peers and capabilities associated to an active call.